setup.py: stop importing Cython in setup.py
setup.py: stop importing Cython in setup.py

This way, it installs properly when Cython is not yet installed. I took
this approach from https://github.com/douban/libmc/pull/45/files.

To test, I create an empty venv, installed qcore in it, and confirmed
that files were correctly Cythonized.

quora/qcore